During surgery and in case of emergency, blood plasma, drugs, saline solutions and glucose are commonly infused into patients. Blood is typically stored in storage bags at a temperature of about 4.degree. C. To infuse the blood the storage bag is suspended above the patient and gravity fed through a flexible intravenous (I.V.) tube. For years, refrigerated blood, plasma and other solutions have been infused while still cold. However, patients who receive as little as two bags of cold blood sometimes become hypothermic which causes stress as the body expends energy to heat the cold fluids, energy which would be better used in combatting infection or in repairing damaged tissue. Cold fluids, at temperatures substantially below normothermic or body temperature, can also cause patients to feel uncomfortably cold as it lowers the temperature of the tissue through which it flows.
To eliminate this problem attempts have been made to heat blood storage bags to normothermic temperature prior to use. However, because the blood travels for some time through the I.V. tube prior to entering the patient, it can cool to below normothermic temperature. This problem cannot be solved by overheating the blood since that is bio-destructive. Also, because a relatively large quantity of blood is heated at one time in the storage bag, blood temperature variances may occur within the bag. If the bag is not heated continuously during transfusion it will cool over time.
Heat exchangers have also been used which circulate refrigerated blood through heated water, as shown in U.S. Pat. Nos. 4,177,816, 4,416,280, and 4,705,508. However, because large amounts of water must be warmed by these exchangers, they are rather inefficient. Their size also often requires that they be located some distance away from patients which once again permits the blood to cool within the I.V. tube between the exchanger and the patient.
As shown in U.S. Pat. No. 4,934,336, devices with heat packs have also been employed. They however require the storage bag and I.V. tube to be meticulously wrapped and unwrapped about device. Also, being exothermically reactive, the blood flow rate effects heating which lessens effective heat control.
Another type of device, shown in U.S. Pat. No. 4,735,609, utilizes a disposable pouch having an inlet and an outlet to which I.V. tubes are coupled and a heater for heating the pouch and fluids in it. Here, however, the coupling of the I.V. tube with the pouch enables air to enter both which must be bled off. This also requires additional sterility measures to be taken.
It thus is seen that a need remains for a heater for use in vivo blood infusions by which refrigerated blood may be heated to normothermic temperature prior to entry into the patient in a more efficient and effective manner. It is to the provision of such therefore that the present invention is primarily directed.